The present invention relates to methods for preparing perhalogenated five-membered cyclic compounds, such as chlorofluorocyclopentenes and chlorofluorocyclopentanes, particularly 1,2-dichlorohexafluorocyclopentene, 1,1-dichlorooctafluorocyclopentane and the like, which are useful as intermediates for heptafluorocyclopentane and as intermediates for various fluorine-containing compounds. Heptafluorocyclopentane is useful as a fluorine-containing detergent, a fluorine-containing drying solvent, or the like.
It is known that hydrogen-containing fluorinated cyclopentanes are produced at first by fluorinating chlorinated cycloalkenes corresponding to the fluorinated cyclopentanes to obtain vicinally chlorinated fluorocyclopentene derivatives, and then by fluorinating and hydrogenating these derivatives. It is known that vicinally chlorinated fluorocyclopentene derivatives are produced by a first method, in which perhalogenated cycloolefins are used as starting materials, or a second method, in which perhalogenated cycloconjugated dienes are used as starting materials. In either of these first and second methods, the fluorination can be conducted by either a liquid phase process or a gas phase process. This liquid phase process can be conducted by using antimony trifluoride or hydrogen fluoride as a fluorination agent, in the presence of an antimony halide as a fluorination catalyst. Antimony halide is, however, highly corrosive. Furthermore, if hydrogen fluoride is used as the fluorination catalyst in an industrial scale production, the reaction pressure may become as high as 10-30 kg/cm.sup.2. This may cause some limitations in the selection of devices. The gas phase process can be conducted by using hydrogen fluoride as a fluorination agent, in the presence of a fluorination agent selected from various substances. U.S. Pat. No. 3,178,482 discloses a method for producing 1,2-dichlorohexafluorocyclopentene by fluorinating trichloropentafluorocyclopentene in the presence of activated carbon as catalyst. U.S. Pat. No. 3,258,500 discloses a method for producing 1,2-dichlorohexafluorocyclopentene by fluorinating 1,2,4-trichloropentafluorocyclopentene in the presence of chromium oxide (CrO.sub.3) as catalyst. DE 1543015 discloses a method for producing 1,2-dichlorohexafluorocyclopentene by fluorinating octachlorocyclopentene in the presence of a Cu/Al oxide.
It is disclosed in J. Am. Chem. Soc., 67, 1235 (1945) to react 1,2-dichlorohexafluorocyclopentene with chlorine at 70.degree. C. under the UV light irradiation in order to saturate its double bond with a halogen except fluorine. It is disclosed in J. of Fluorine Chem., 49(3), 385-400 (1990) to produce 1,2 dichlorooctafluorocyclopentane by fluorinating 1,2-dichlorohexafluorocyclopentene at 25.degree. C. in the presence of vanadium pentachloride. Japanese Patent First Publication JP-A-8-333285 discloses a method for producing 1,2-dichlorohexafluorocyclopentene at first by reacting hexachlorocyclopentadiene with chlorine in the presence of antimony trichioride, thereby to respectively convert the hexachlorocyclopentadiene and antimony trichloride to octachlorocyclopentene and antimony pentachloride, and then by adding hydrogen fluoride thereto. JP-A-3-151336 discloses a method for fluorinating hexachlorocyclopentadiene in a gas phase in the presence of chlorine and hydrogen fluoride using a Mg/Bi/Fe oxide as a catalyst, thereby to obtain 1,2-dichlorohexafluorocyclopentene. It is, however, necessary to previously fluorinate such oxides, which are disclosed in JP-A-3-151336 and U.S. Pat. No. 3,258,500, if they are used as fluorination catalysts. This fluorination takes a long time, and it is difficult to achieve a complete fluorination.
One of the aimed products of the invention, that is, 1,1-dichlorooctafluorocyclopentane, is a useful compound, since it can easily be reduced by hydrogen to beptafluorocyclopentane. A method for producing 1,1-dicholorooctafluorocyclopentane is disclosed in U.S. Pat. No. 5,416,246. In this method, it is produced through isomerization of 1,2-dichlorooctafluorocyclopentane by passing 1,2-dichlorooctafluorocyclopentane, together with hexafluoropropene, through chlorofluorinated aluminum heated at 130.degree. C.